Zyrtec (Cetirizine) vs. Benadryl (Diphenhydramine)
Medically reviewed by Erika Prouty, PharmD
Benadryl (diphenhydramine) and Zyrtec (cetirizine) are over-the-counter (OTC) antihistamines commonly used to treat allergy symptoms. Although similar in their uses, Benadryl and Zyrtec have a few distinct differences.
Benadryl is a first-generation antihistamine, whereas Zyrtec is a second-generation antihistamine, belonging to a newer class of antihistamines. These two types of antihistamines work differently. For example, first-generation antihistamines like Benadryl are more likely to cause drowsiness.
Benadryl is also shorter-acting, so it must be taken multiple times daily, whereas Zyrtec will last all day after a dose.
This article will discuss similarities and differences between Benadryl and Zyrtec, including dosing, side effects, safety, and drug interactions.
Getty Images / EHStock
Zyrtec vs. Benadryl: What Do They Do?
Zyrtec and Benadryl are both antihistamines that temporarily relieve allergy symptoms like runny nose, sneezing, itchy, watery eyes, and an itchy nose and throat caused by seasonal allergies or other allergens.
They can also be used to treat chronic urticaria (long-term hives). Both are available OTC (without a prescription) and as generic products.
To understand how antihistamines work, it's important to know how the immune system reacts to allergens (substances causing an allergic reaction).
When your body encounters an allergen, it releases a chemical called histamine. Histamine triggers symptoms of runny nose and congestion. Drugs that block the histamine H1 receptor relieve symptoms associated with allergies.
Benadryl, a first-generation antihistamine, has been around since 1946. However, Zyrtec belongs to a newer class of medications called second-generation antihistamines.
First-generation antihistamines like Benadryl cross into the central nervous system (CNS) and cause drowsiness. Because of this side effect, diphenhydramine is commonly used in OTC sleep aids like Tylenol PM, which also contains acetaminophen.
Newer antihistamines like Zyrtec work against histamine receptors outside the brain; therefore, they cause less drowsiness than Benadryl.
How to Take Zyrtec and Benadryl
Benadryl is available in 25 milligram (mg) tablets or capsules and as a liquid. Its typical dosing recommendations are:
Adults and children 12 years and older: Take 25 to 50 mg of Benadryl every four to six hours.
Children under 12 years: Consult your child's healthcare provider for a specific weight-based dose.
Because Benadryl causes drowsiness, some people take it only at bedtime and not during the day.
Zyrtec is available in 5 and 10 mg tablets and as a liquid. Dosing recommendations for Zyrtec include:
Adults and children 6 years and older: Take 10 mg once a day.
For children under 6 years: Consult a healthcare provider.
Both Benadryl and Zyrtec may be taken with or without food. Both medications can be taken on an as-needed basis, meaning you can take them when needed to relieve symptoms and stop when you no longer need them.
Zyrtec vs. Benadryl: Onset and Duration of Effects
Zyrtec has a longer duration of action than Benadryl; therefore, you only need to take it once a day. Benadryl does not last as long, so it needs to be taken every four to six hours.
Both start working quickly, within 15 to 60 minutes of dosing.
Side Effects
Common side effects of Benadryl include:
Drowsiness
Dry mouth, nose, or throat
Dizziness
Nausea or vomiting
Loss of appetite
Constipation
Headache
Excitement (especially in children)
Serious side effects:
Visual disturbances
Urinary problems
The most common side effect of Zyrtec is drowsiness (14% vs. 6% with placebo) with higher doses. Other side effects are fatigue, dry mouth, sore throat, and dizziness.
Aside from dry mouth, Zyrtec does not commonly cause other “drying” side effects like dry eyes, dry throat, constipation, and urinary retention that can be seen with Benadryl.
Safety
Diphenhydramine is a common active ingredient used in multi-ingredient OTC products for cold and allergy symptoms. Read the package labeling carefully to be sure you are not taking more diphenhydramine than the recommended dose from all sources.
Know how the medication affects you before driving a car or any other activity requiring alertness. Drinking alcohol can increase the drowsiness caused by these medications, so avoid alcohol during this time.
People over 65 should generally avoid taking diphenhydramine due to a greater risk of side effects, such as:
An increased risk of falls
Cognitive impairment
Confusion
Drying effects (dry mouth, constipation, urinary retention)
Which Is More Effective?
Both Zyrtec and Benadryl are effective in reducing allergy symptoms.
Studies show that Zyrtec is as effective as Benadryl in treating allergic reactions to chemotherapy treatments and food-induced allergic reactions.
Zyrtec tends to cause less sedation than Benadryl, though it is important to note that reactions to a medication can vary by person.
Interactions
In Benadryl and Zyrtec, drugs that cause central nervous system (CNS) depression may cause additive CNS reactions if taken simultaneously.
Other drugs that interact with Benadryl include:
Drugs with anticholinergic effects, such as Gocovri (amantadine), amitriptyline, and Spiriva (tiotropium): These may worsen the anticholinergic side effects of Benadryl, such as dry mouth and constipation. Anticholinergic medications block a neurotransmitter called acetylcholine in the body.
Morphine and other opioid pain medications: Benadryl can increase the effects of opioids in the body.
Additionally, you should not use two antihistamines at the same time, as this can increase the risk of side effects.
Related: Can You Take Zyrtec and Benadryl Together?
Summary
Benadryl and Zyrtec are both OTC antihistamines used to relieve the symptoms of allergies or minor allergic reactions.
Most people find Zyrtec less sedating than Benadryl, but you should use caution when taking either of them for the first time until you know how your body reacts. Zyrtec is a good choice if you want to take medication less frequently, as it is dosed once daily.
The main drug interaction to be aware of is other drugs that also cause drowsiness, as these effects add up.
Frequently Asked Questions
Can I use Zyrtec or Benadryl while pregnant?
Yes, usually. Both Zyrtec and Benadryl are generally considered safe during pregnancy. If you are pregnant, talk with your healthcare provider about which medications are OK to take.
Can I take Zyrtec for an allergic reaction?
Yes. Zyrtec is effective for treating minor allergic reactions to chemicals, environmental allergens, foods, and drugs. It is important to note that epinephrine remains the primary treatment for anaphylactic reactions, which is not an ingredient in Zyrtec.
Can you take Zyrtec and Benadryl together?
People usually take just one antihistamine at a time. No data suggest that taking Benadryl and Zyrtec together is more effective than taking one at a time. Furthermore, there is a risk of increased side effects, especially drowsiness and impaired coordination.
Read the original article on Verywell Health.
